[mythtv-users] AC3, Analog Cable and 5.1

Michael Heironimus mkh01 at earthlink.net
Thu Mar 23 02:04:04 UTC 2006

On Wed, Mar 22, 2006 at 06:46:46PM -0500, White Joe wrote:
> I found this thread that implies that some NTSC broadcasts may be
> decodable into 5.1 using Dolby Prologic.  Is this true?  Practical?
> Prevalent? Relevant?
> http://www.gossamer-threads.com/lists/mythtv/users/160633?search_string=
> dolby%205.1%20analog;#160633

It's not 5.1. Audio encoded with Dolby Surround can be decoded by a
Dolby Prologic receiver for 4-channel playback (left, right, center,
rear). Newer receivers may have Prologic II decoders, which allow 5
channel (left, right, center, left-rear, and right-rear). In either
case, the extra channel information is encoded in a normal stereo signal
and can be sent over analog cable. Any device that records the stereo
signal with sufficient quality should give you 4 channel audio when you
play it back as long as you have Prologic decoding enabled on your

That being said, very few TV programs make any real use of Dolby
Surround. When I play a DVD I'm surprised if it doesn't have at least 4
channel audio, but I'm even more surprised when a TV show on cable has
anything on the rear channel. Usually almost everything is through the
center channel.

Michael Heironimus

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